Electric machine, especially a generator for motor vehicles

ABSTRACT

An electric machine, particularly a generator for motor vehicles, includes a housing and a casing enclosing the housing concentrically, the casing, together with the housing, bounding an annular space that is sealed in a fluid-tight manner and is connected to a coolant outflow and a coolant inflow. To achieve a uniform circumflow of the housing with sufficient cooling capacity, even given low volumetric flow of the coolant, a plurality of axial guide bars are arranged in the annular space, so that the coolant restrictedly flows in an axially wide-strip manner through the annular space within space segments arranged in a row in the circumferential direction, with an opposing flow direction in successive space segments.

FIELD OF THE INVENTION

The present invention relates to an electric machine, particularly agenerator for motor vehicles.

BACKGROUND INFORMATION

In a conventional water-cooled generator for motor vehicles, for exampleas described in French Patent Application No. 2 717 638, the stator androtor are accommodated in a pot-shaped housing which, on one hand, isinserted into a pot-shaped encasing in such a manner that an annularspace remains between the covering of the pot-shaped encasing and theouter surface of the housing, the annular space being covered in afluid-tight manner on one side by the bottom of the encasing, and on theother side, by a cover mounted on the pot edge of the encasing andhousing. The annular space, on sides turned away from each other,includes an inflow orifice and a discharge orifice which are eachenclosed by a connecting piece, projecting radially on the encasing, fora water pipe. The water circulated by a pump in a circulation circuitenters into the annular space through the inflow orifice, circumflowsthe housing, and exits the annular space again via the dischargeorifice. The heat emitted by the generator is absorbed by the coolerwater and carried away.

SUMMARY OF THE INVENTION

The electric machine of the present invention may provide that, due tothe forced guidance of the coolant by the guide bars, a uniformcircumflow of the housing of the electric machine by the coolant isensured, so that the formation of so-called “hot spots” due to locallyinsufficient flow velocity of the coolant, for example, due to thedevelopment of recirculation bubbles, is prevented. Due to the multitudeof guide bars, which at the same time act as cooling vanes, the housingsurface available for heat transfer to the coolant increases, so thatfor an equal cooling capacity, the volumetric flow of the coolant may bereduced by the factor by which the housing surface is increased. Due tothe wide-strip axial flow of the coolant, which in each case is turnedaround at the end sides of the annular space, at the location where thestator of the machine supplies a large input of heat through themetallic housing, the surface for the heat transfer and the flowvelocity of the coolant are also great, so that the local coolingcapacity is well adapted to the local heat input. The spacings of theguide bars may be dimensioned accordingly for this purpose, as well.Short-circuit losses due to leakage currents over the guide bars arelow, since due to the configuration which is favorable for the flow, nolarge pressure differences result across the small gaps present betweenthe covering and the outer surface of the guide bars.

All in all, in the example machine of the present invention,sufficiently great cooling capacity is furnished for heat dissipation inall space segments, and indeed also for the cases when only a limitedvolumetric flow of the coolant is available.

According to an example embodiment of the present invention, the guidebars in each space segment form a plurality of parallel flow channelshaving in each case an inflow end and an outflow end. In the annularspace, at each end of the flow channels, coolant collecting sections areformed, extending in the circumferential direction, of which in eachcase one inflow collecting section extends over the inflow ends and oneoutflow collecting section extends over the outflow ends of each spacesegment. At each end of the flow channels, adjoining the dischargecollecting section of the one space segment in the circumferentialdirection is an inlet collecting section of the following space segment,each inlet collecting section being separated from the dischargecollecting section of the space segment following in the flow direction.This parallel arrangement of the guide bars in a few, e.g., five, spacesegments distributed over the periphery of the housing reduces thelength of the cooling channel and the resistance to flow.

According to an example embodiment of the present invention, the coolantcollecting sections are formed in such a manner that the cross-sectionof the inlet collecting sections decreases in the flow direction, andthe cross-section of the discharge collecting sections increases in theflow direction. Due to this structural formation, the flow velocity inthe region of the re-routing of the coolant flow is reduced, and coolantis uniformly distributed to the parallel flow channels, accompanied byuniform flow velocity in the flow channels.

In an example embodiment of the present invention, the coolantcollecting sections at the ends of the flow channels are formed in themanner that the guide bars have an equal length, and that within a spacesegment, successive guide bars in the circumferential direction areshifted axially—e.g., by equal amounts—in the same direction relativelyto each other. In so doing, the last guide bar in the space segment isshifted so far that it is brought forward with one bar end to one of twoannular bars terminating the annular space at the end face. Due to thisstructural configuration, the desired decrease and increase ofcross-section in the coolant collecting sections and the separation ofthe inflow collecting sections from the outflow collecting sections inthe following space segment may be implemented from the standpoint ofproduction engineering.

According to an example embodiment of the present invention, an inflowchannel extending in the axial direction and connected to the coolantinflow, and an outflow channel extending in the circumferentialdirection and connected to the coolant outflow are formed between thefirst guide bar of the first space segment in the flow direction and thelast guide bar of the last space segment. The inflow and outflowchannels are separated from each other by a separating bar extending inthe circumferential direction from the front end of the last guide barin the last space segment up to the first guide bar in the first spacesegment. In this context, an inflow connecting piece for the coolantinflow mounted on the casing is aligned with its axis in such a mannerthat the axis forms an obtuse angle with the axial flow direction of thecoolant in the inflow channel, and an outflow connecting piece for thecoolant outlet mounted on the casing is implemented so that its axisforms an obtuse angle with the more or less tangential flow direction inthe outflow channel. Due to this guidance of the inflow and outflow ofthe coolant, the pressure at the separating bar is reduced on thehigh-pressure side by the volumetric flow directed away from theseparating bar. On the low-pressure side, the pressure at the separatingbar is increased by the dynamic pressure of the upwardly dischargingcoolant. All in all, the result thereby on one hand is a reduction ofthe total pressure over the separating bar, so that only extremely lowleakage losses occur, and on the other hand, a feed and discharge of thecoolant which is favorable to the flow, thus helping to reduce the flowresistance.

According to an example embodiment of the present invention, the guidebars, one annular bar and the separating bar, are integrally molded onthe housing, which is produced using pressure diecasting or injectionmolding techniques. Due to the bar formation, which is selected to befavorable from a standpoint of production engineering, the pressure orinjection mold is able to be drawn off in the axial direction. Thecasing, produced separately with integrally molded annular bar, is slidonto the housing thus produced, and the annular space is sealed by twoO-rings between the housing and the casing in the region of the annularbars.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal section of a generator for motor vehicles ina cutaway view.

FIG. 2 shows a perspective view of the generator in the direction ofarrow II in FIG. 1 in a cutaway view.

FIG. 3 shows a plan view of the generator in FIG. 1, with the casingdrawn off, in a perspective representation.

FIG. 4 shows a developed view of the housing of the machine in FIGS.1-3.

DETAILED DESCRIPTION

The generator, shown in longitudinal section in a cutaway view in FIG.1, for a motor vehicle as an example embodiment for a general electricmachine includes, a stator 11, accommodated in a housing 10, including astator winding 12, and a rotor 14, enclosed concentrically by stator 11leaving an air gap 13, which sits in a rotationally fixed manner on arotor shaft 15 rotationally mounted in housing 10. Housing 10 ispot-shaped, including a base part 101 and a cylindrical part 102. Oncylindrical part 102, at the end facing away from base part 101, aradial flange 103 is integrally formed, upon which a bearing cover 16 issecured, sealing housing 10 at the front end. Rotor shaft 15—as notshown in FIG. 1—is in each case accommodated in a pivot bearingintegrated in base part 101 and in bearing cover 16.

Directly adjacent to flange 103, an annular bar 104 is integrallymolded, projecting radially from the surface of cylindrical part 102.From the other end of cylindrical part 102, a separately manufactured,hollow-cylindrical casing 17 is slid onto housing 10 and, with its frontend in the push-in direction, overreaches annular bar 104 on one side,and abuts against flange 103 on the other side. At the rear end ofcasing 17, a radially inwardly projecting annular bar 171 is integrallyformed, whose radial height corresponds to the radial height of annularbar 104 on housing 10. In this manner, an annular space 18 is boundedbetween casing 17 and cylindrical part 102 of housing 10 and is sealedat the end faces by the two annular bars 104 and 171. In the region ofannular bars 104 and 171, in each case a ring seal 19 in the form of anO-ring is disposed between casing 17 and cylindrical part 102 of housing10, in each instance a ring seal 19 fitting in an annular groove 20 cutinto cylindrical part 102 of housing 10. Annular space 18 is connectedto a coolant inflow 21 and a coolant outflow 22, which are each assignedan inflow connecting piece 23 and outflow connecting piece 24,respectively, arranged outside on casing 17.

To ensure a uniform circumflow of the housing by the coolant, arestricted guidance of the coolant is implemented in annular space 18from coolant inflow 21 to coolant outflow 22. In this context, thecoolant is restrictedly guided by a plurality of axial guide bars 25, sothat it flows in an axially wide-strip manner through annular space 18within segments of the annular space 18 that are arranged in a row inthe circumferential direction, hereinafter known as space segments 26,with opposing flow direction in successive space segments 26. Guide bars25 have a radial bar height corresponding to the radial width of annularspace 18, and in the example embodiment, having the same cross-sectionand same axial length, are arranged parallel and equidistant to eachother, as may be seen in FIGS. 3 and 4. In the example embodimentdescribed here, guide bars 25 are divided over a total of five spacesegments 26; however, the number of space segments 26 may be selected asdesired. In each space segment 26, guide bars 25 form between themselvesa plurality of parallel flow channels 27 including an inlet end 271 anda discharge end 272, which have an equal flow cross-section. Guide bars25 may also be configured and arranged in such a manner, for example,with differently sized distances between them, that flow channels 27enclosed by them have different flow cross-sections. In this context,the different flow cross-sections are spatially allocated in adaptationto locally different heat input into housing 10. Within each spacesegment 26, inlet ends 271 lead into an inlet collecting section 28 anddischarge ends 272 lead into a discharge collecting section 29, so thatat each end of flow channels 27, adjoining in each case a dischargecollecting section 29 of the one space segment 26 in the circumferentialdirection is an inlet collecting section 28 of the following orpreceding space segment 26. In inlet collecting sections 28 anddischarge collecting sections 29, known altogether as coolant collectingsections, the coolant is distributed to individual flow channels 27 inspace segment 26, i.e., the coolant emerging from flow channels 27 iscombined and turned around in its flow direction. To avoid short-circuitcurrents or leakage currents from inlet collecting section 28 of the onespace segment 26 to discharge collecting section 29 of space segment 26following in the flow direction, in each case inlet collecting section28 of the one space segment 26 is separated from discharge collectingsection 29 of space segment 26 following in the flow direction. As FIGS.3 and 4 show, coolant collecting sections 28, 29 are configured in sucha manner that each cross-section of inlet collecting sections 28decreases in the flow direction, and each cross-section of dischargecollecting sections 29 increases in the flow direction. The coolantcollecting sections with their cross-sections changing in the flowdirection are realized in the manner that parallel guide bars 25following one another in the circumferential direction within a spacesegment 26 are shifted axially by an amount, e.g., by the same amount ineach case, in the same direction relative to each other. In so doing,the last guide bar 25 in each space segment 26 is shifted so far thatwith one of its two bar ends, it abuts against one of annular bars 104and 171, respectively, and consequently separates inlet collectionsection 28 from discharge collecting section 29 of space segment 26following in the flow direction.

As may be seen in FIGS. 3 and 4, between first guide bar 251 of firstspace segment 261 in the flow direction and last guide bar 252 of lastspace segment 262 in the flow direction, an inflow channel 30 is formedthat is connected to coolant inflow 21 and extends in the axialdirection, and an outflow channel 31 is formed that is connected tocoolant outflow 22 and extends in the circumferential direction. Inflowchannel 30 and outflow channel 31 are separated from each other by aseparating bar 32 extending in the circumferential direction from thefront end of last guide bar 252 in last space segment 262, up to firstguide bar 251 in first space segment 261. To reduce the total pressureprevailing at separating bar 32, and consequently to avoid possibleleakage losses via the small gap which may form between the bar surfaceof separating bar 32 and the inner surface of casing 17, or to keep theleakage losses very small, inflow connecting piece 23 is formed in sucha manner that its axis forms an obtuse angle α with the axial flowdirection of the coolant in inflow channel 30, as is symbolized in FIG.3 by inflow arrow 33 (see also FIG. 2). On the other hand, outflowchannel 31 is formed in such a manner that its axis runs more or lesstangentially with respect to housing 10, or in its circumferentialdirection, and forms an obtuse angle β with the flow direction inoutflow channel 31, as is symbolized in FIG. 3 by outflow arrow 34 (seealso FIG. 2).

The arrangement of guide bars 25 and flow channels 27 formed betweenguide bars 25 may be seen very well in the developed view of housing 10shown in FIG. 4. The flow of the coolant in individual flow channels 27and in the coolant collecting sections at flow ends 271 and 272 of flowchannels 27 is symbolized by the flow arrows drawn in in FIG. 4.

Housing 10, together with parallel guide bars 25, separating bar 32 andannular bar 104, may be produced using the pressure diecasting orinjection molding method. Due to the structural configuration of housing10, the pressure or injection mold is then able to be drawn off axially,and after the generator is completed, separately produced casing 17 maybe slid so far onto housing 10 that the front end face of casing 17 inthe push-in direction strikes against flange 103 formed on cylindricalpart 102 of housing 10. Housing 10 and casing 17 are held together byfastening screws 35 which are screwed through flange 103 into the endface of casing 17. At the same time, screws 35 also affix bearing cover16 on flange 103 (FIGS. 1 and 2).

1. An electric machine, comprising: a housing; a casing which enclosesthe housing concentrically and which, together with the housing, boundsan annular space that is sealed in a fluid-tight manner and is connectedto a coolant inflow and a coolant outflow; and a plurality of axialguide bars arranged in the annular space in such a manner that a coolantrestrictedly flows in an axially wide-strip manner within space segmentsarranged in a row in a circumferential direction, with an opposing flowdirection in successive space segments.
 2. An electric machine,comprising: a housing; a casing which encloses the housingconcentrically and which, together with the housing, bounds an annularspace that is sealed in a fluid-tight manner and is connected to acoolant inflow and a coolant outflow; and a plurality of axial guidebars arranged in the annular space in such a manner that a coolantrestrictedly flows in an axially wide-strip manner within space segmentsarranged in a row in a circumferential direction, with an opposing flowdirection in successive space segments; wherein in each of the spacesegments, the plurality of axial guide bars form a plurality of parallelflow channels having, in each case, an inlet end and an outlet end,wherein the plurality of axial guide bars are arranged in the annularspace so that at each end of the plurality of parallel flow channels,coolant collecting sections are formed extending in the circumferentialdirection, of which in each case one inlet collecting section extendsover the inlet end and one discharge collecting section extends over theoutlet end of the plurality of parallel flow channels of each spacesegment, wherein at each end of the plurality of parallel flow channels,adjoining a discharge collecting section of the space segment in thecircumferential direction is an inlet collecting section of a followingspace segment, and wherein each inlet collecting section is separatedfrom the discharge collecting section of the space segment following ina flow direction.
 3. The electric machine of claim 2, wherein theelectric machine is a generator for a motor vehicle.
 4. The electricmachine of claim 2, wherein the plurality of axial guide bars have aradial bar height corresponding to a radial width of the annular space.5. The electric machine of claim 2, wherein the coolant collectingsections are formed in such a manner that a cross-section of the inletcollecting sections tapers in the flow direction, and a cross-section ofthe discharge collecting sections increases in the flow direction. 6.The electric machine of claim 5, wherein the cross-sections of theplurality of parallel flow channels formed between the plurality ofaxial guide bars are of equal size.
 7. The electric machine of claim 5,wherein the cross-sections of the plurality of parallel flow channelsformed between the plurality of axial guide bars are dimensioned withdifferent size in adaptation to a heat dissipation to be performeddifferently locally.
 8. The electric machine of claim 2, wherein thecoolant collecting sections at ends of the plurality of parallel flowchannels are formed in a manner that the plurality of axial guide barshave a same length, and within a space segment, successive guide bars inthe circumferential direction are shifted axially by equal amounts in asame direction relative to each other.
 9. The electric machine of claim8, wherein a last axial guide bar of the plurality of axial guide barsin the space segment is brought forward with one bar end up to one oftwo annular bars sealing the annular space at an end face.
 10. Anelectric machine, comprising: a housing; a casing which encloses thehousing concentrically and which, together with the housing, bounds anannular space that is sealed in a fluid-tight manner and is connected toa coolant inflow and a coolant outflow; and a plurality of axial guidebars arranged in the annular space in such a manner that a coolantrestrictedly flows in an axially wide-strip manner within space segmentsarranged in a row in a circumferential direction, with an opposing flowdirection in successive space segments; wherein between a first axialguide bar of the plurality of axial guide bar of a first space segmentin a flow direction and a last axial guide bar of the plurality of axialguide bars of a last space segment, an inflow channel is formedextending in an axial direction and connected to the coolant inflow, andan outflow channel is formed extending in the circumferential directionand connected to the coolant outflow, the inflow channels and outflowchannels are separated from each other by a separating bar extending inthe circumferential direction from the last axial guide bar in the lastspace segment up to the first axial guide bar in the first spacesegment.
 11. The electric machine of claim 10, wherein the coolantinflow includes an inflow connecting piece mounted on the casing whoseaxis forms an obtuse angle with an axial flow direction of a coolant inthe inflow channel.
 12. The electric machine of claim 10, wherein thecoolant outflow includes an outflow connecting piece mounted on thecasing whose axis forms an obtuse angle with a flow direction in theoutflow channel pointing in the circumferential direction of thehousing.
 13. The electric machine of claim 10, wherein the plurality ofaxial guide bars, the separating bar and one of two annular bars sealingthe annular space at an end face are integrally molded on the housing.14. The electric machine of claim 13, wherein the casing is produced asa separate component on which another one of the two annular bars isintegrally molded, the housing is inserted into the casing, and a ringseal is disposed between the housing and the casing in a region of thetwo annular bars.
 15. The electric machine of claim 14, wherein the ringseal is inserted in an annular groove introduced into the housing. 16.An electric machine, comprising: a housing; a casing which encloses thehousing concentrically and which, together with the housing, bounds anannular space that is sealed and is connected to a coolant inflow and acoolant outflow; and axial guide bars arranged in the annular space sothat a coolant restrictedly flows in an axially wide-strip manner withinspace segments arranged in a row; wherein in each of the space segments,the axial guide bars form flow channels each having an inlet end and anoutlet end, wherein the axial guide bars are arranged in the annularspace so that at each end of the flow channels, coolant collectingsections are formed, of which in each case one inlet collecting sectionextends over the inlet end and one discharge collecting section extendsover the outlet end of the flow channels of each space segment, whereinat each end of the flow channels, adjoining a discharge collectingsection of the space segment is an inlet collecting section, and whereineach inlet collecting section is separated from the discharge collectingsection of the space segment.
 17. An electric machine, comprising: ahousing; a casing which encloses the housing and which, together withthe housing, bounds an annular space that is sealed and is connected toa coolant inflow and a coolant outflow; and axial guide bars arearranged in the annular space so that a coolant restrictedly flows in anaxially wide-strip manner within space segments arranged in a row;wherein between a first axial guide bar of the axial guide bar of afirst space segment in a flow direction and a last axial guide bar ofthe axial guide bars of a last space segment, an inflow channel isformed extending in an axial direction and connected to the coolantinflow, and an outflow channel is formed extending in thecircumferential direction and connected to the coolant outflow, theinflow channels and outflow channels are separated from each other by aseparating bar.